Bootcamp Win installed on external SSD - Win won't recognize MBP internal SSD formatted ExFat or NTFS

No, and I am at a loss as to why. Although the internal SSD shows up under Win, when I try and copy/move something to the internal SSD drive (e: or f:), even if it appears to copy, it does not in fact do so when I log back in on the OS side.

Originally, I had a single SSD divided into 3 partitions: 1 - Mac; 1 - Win; 1 - ExFat for common storage. Life was good. Then my SSD died and I had to replace it; about the same time Catalina came upon the scene. Trying to create standard Bootcamp partition on the internal SSD became impossible (see all the other comments about Win not installing under Bootcamp). So, I opted to load Win on an external SSD. Sounded good, but I can no longer access the internal SSD for the ExFat partition for common storage. This also play out with restoring from an Acronis backup because Acronis doesn't see the internal SSD.

I thought it might be a sharing problem, so I have granted sharing, but to now avail.

Files:

A file copied to Data HD under OS will show up in Data HD under Win. However, it is not openable. (I've tried both txt and jpg.)

A file copied to Data HD under Win will NOT show up in Data HD under OS. And, if I log out of Win and then back in, the file will no longer be in Data HD under Win.

Interestingly, while I cannot copy any files into the Win HD (external SSD) under OS (which makes sense since it is formatted NTFS), I can read and copy files from Win HD to the OS desktop (internal SSD).

Also interesting, if I try and copy a file on the Win side (ext SSD) to the BOOTCAMP folder (empty partition, but formatted NTFS) I get an error message. This is an attempted NTFS to NTFS.

Other NTFS third-pty software installed on external drive (Win):

Google Backup

Acronis

ExpressVPN

Malwarebytes

Teamviewer

They all seem to run, but Acronis, a backup program, while it sees the internal drives, it is unable to access then to "save f: to c:" or "c: to f:".

I totally agree. His updated 2020 version of setting up Bootcamp on an SSD was probably the best "how to" YouTube I've ever watched. He left nothing out. And, I too, had to sort of manually load the drivers for Bootcamp. The exe file to load drivers got hung up on the ATI driver. When I forced this individual load to cancel with Task Manager, all the rest loaded without error.

However, even though I have Win up and humming on my external SSD, I am having issues inter-relating with the internal SSD.

From the Win side:

Any insight greatly appreciated.

Okay.

From the Mac side (internal SSD):

And from the Window's side (external SSD):

Yes.

I am assuming you're talking about copying in Win, F: to C:.

First attempt squawked about Admin privilege.

But still failed even after clicking "continue".

I can see why re-lettering disks would be asking for problems.

No, I did not manually assign drive letters. They were automatically assigned. However, based upon your question, I did change drive letters on both via Window's Disk Management. The letters readily changed and stuck through a restart. An attempt to copy a file from C: to P: was as unsuccessful as before when the drive was F:. *sigh* I have since returned the drive letters to their original state.